Hydrazine functionalized probes for chromogenic and fluorescent ratiometric sensing of pH and F−: experimental and DFT studies

Abstract

Two novel hydrazine based sensors, BPPIH (N¹,N³-bis(perfluorophenyl)isophthalohydrazide) and BPBIH (N^1′,N^3′-bis(perfluorobenzylidene)isophthalohydrazide), are presented here. BPPIH is found to be a highly sensitive pH sensor in the pH range 5.0 to 10.0 in a DMSO–water solvent mixture with a pK_a value of 9.22. Interesting optical responses have been observed for BPPIH in the above mentioned pH range. BPBIH on the other hand turns out to be a less effective pH sensor in the above mentioned pH range. The increase in fluorescence intensity at a lower pH for BPPIH was explained by using density functional theory. The ability of BPPIH to monitor the pH changes inside cancer cells is a useful application of the sensor as a functional material. In addition fluoride (F⁻) selectivity studies of these two chemosensors have been performed and show that between them, BPBIH shows greater selectivity towards F⁻. The interaction energy calculated from the DFT-D3 supports the experimental findings. The pH sensor (BPPIH) can be further interfaced with suitable circuitry interfaced with desired programming for ease of access and enhancement of practical applications.